Estimation of the phosphorus requirement of weanling pigs fed supplemental phytase

Studies were conducted with crossbred weanling pigs to determine the level of phosphorus needed to be fed when a maize–soyabean meal–whey diet was supplemented with exogenous phytase (Natuphos?). In Trial 1, phytase was added at 1200 phytase units (PTU) kg^?1 as phosphorus decreased. The control diet in Phase I (0–14 days) contained 7.3 g kg^?1 phosphorus and in Phase II (14–28 days) contained 6.5 g kg^?1 phosphorus. Dietary phosphorus was calculated to decrease by 0.8, 1.6 or 2.4 g kg^?1 when phytase was supplemented. Chromic oxide was added for estimation of apparent absorption of phosphorus. Performance was optimum when 5.7 and 4.8 g kg^?1 phosphorus (analysed levels) were fed with 1200 PTU kg^?1 phytase in Phases I and II, respectively. The lowest dietary phosphorus levels did not reduce performance for the overall 28-day period. Apparent phosphorus digestibility was increased by phytase in Phase I when 5.7 g kg^?1 phosphorus was fed compared to the control diet and in Phase II when 6.0 g kg^?1 phosphorus was fed with phytase. Faecal phosphorus excretion decreased in both phases as dietary phosphorus decreased. Faecal phosphorus excretion was minimized at the lowest phosphorus level with no decrease in performance. The estimated requirement for dietary phosphorus, as determined by the NLIN procedure, is 5.0 g kg^?1 in Phase I and 4.3 g kg^?1 in Phase II when 1200 PTU kg^?1 is used. In Trial 2, phytase was supplemented at 500 PTU kg^?1 when phosphorus was decreased in the diet. The control diet contained 6.6 and 6.0 g kg^?1 phosphorus in Phases I and II, respectively, and phosphorus was calculated to decrease by 0.5, 1.0, 1.5, or 2.0 g kg^?1 when phytase was added. Daily gain decreased when 5.0 g kg^?1 phosphorus was fed in Phase I and when 4.6 or 4.2 g kg^?1 (analysed levels) phosphorus was fed in Phase II with 500 PTU kg^?1. Faecal phosphorus excretion decreased as dietary phosphorus decreased, but there were no treatment effects on apparent phosphorus digestibility. The dietary phosphorus requirement was estimated to be 5.7 and 5.0 g kg^?1 in Phases I and II, respectively, when phytase is fed at 500 PTU kg^?1. At the present recommendation of 500 PTU kg^?1 in starter feed, phosphorus can be decreased by 0.10 g kg^?1. However, higher levels of phytase are needed to actually increase apparent phosphorus digestibility.